Power System Quality Improvement using Doubly-fed Rotary Frequency Converter

Keywords

Wind generation, rotary frequency converter, flywheel

Abstract

An application of rotary frequency converter for a wind
farm system is proposed in this paper. Wind power is
getting attention for prospective renewal energy sources,
and introduction of wind farm generation will solve
environmental matters and energy exhaust problem.
However, the quality of power system frequency will be
degraded as the capacity of wind power generator
increases. Attenuation of mismatch between the served
power and load demand is most important problem in
order to increase number of wind generators.

A wind firm is connected to the proposed rotary
frequency converter as a buffer to connect the wind farm
and the power system. This provides energy storage
function of the output power associated with irregular
wind power. The converter has a synchronous generator
and a doubly-fed machine. The synchronous motor is
connected to the wind farm to supply AC voltage for
induction generators of wind power generation units. The
shaft of the doubly-fed machine is mechanically jointed to
the synchronous motor, and rotates together. Tuning the
current of the secondary winding supplied by
cycloconverter or self-commutated inverter controls the
output power. At present, doubly-fed machine is
commonly used in pumped storage hydraulic power
plants recently constructed. The proposed scheme is an
expansion from the present application.

In order to evaluate the proposed scheme, firstly, load
reference simulation test is carried out for discussion of
the power exchange response to a power grid. Secondly,
experimental study is discussed in order to identify the
required capacity for the rotary frequency converter to
improve the frequency quality. These studies show
preferable characteristic for the viewpoint of power
system quality improvement.